It will be much easier to do this on a new install than try to do in an existing install. Though you can do it, you will have a lot more pain to try to convert an existing install. Better just to export then import any existing content.

And if at all possible, get a different hosting account. Most of the WordPress people on the Linkedin WordPress group talk about how GoDaddy overloads servers and you especially don't want an overloaded shared server for Multisite. Maybe you'll consider getting a new account for this? I'm a fan of A Small Orange web hosting in no small part due to the fact they have a US$25/year account with 150Mb of storage (and they have been my webhost for 5+ years.) But almost any website will do you better than GD.